1. The Field of the Invention
The present invention relates to a nozzle having vanes configured for controlling the amount and direction of roll of a rocket-propelled vehicle by guiding the flow of combustion products as they exit the vehicle. More particularly, the present invention relates to a vectorable nozzle having vanes mounted within an exit cone for guiding the flow of combustion products and thereby controlling roll at velocities which are too low and at angles of attack which are too high to permit effective roll control with aerodynamic fins.
2. Technical Background
Missiles and other vehicles that are propelled by rocket motors are normally equipped with a guidance mechanism to provide control over the yaw, pitch, and roll of the vehicle during flight. The ability to maintain control over the yaw, pitch, and roll of a vehicle is critical to ensuring that the vehicle will maintain a predetermined flight path. Even during high-angle-of-attack maneuvers, requiring substantial change in pitch, roll control must be maintained. For example, a high-angle-of-attack maneuver may be attempted to allow a vertically-launched surface missile to immediately pitch over to follow a generally horizontal flight path. A high-angle-of-attack maneuver is also desirable to permit an air-launched "dogfight" missile to execute a tight turn immediately after launch.
However, conventional guidance mechanisms generally do not provide satisfactory roll control during high-angle-of-attack maneuvers. For example, many conventional guidance mechanisms utilize a vectorable nozzle, generally referred to as a "thrust vector control" ("TVC") nozzle. TVC nozzles operate by positioning the nozzle at a desired angle with respect to the vehicle to alter the vector at which combustion products exit the vehicle. Changing the thrust vector by repositioning the nozzle alters the direction of the forces acting on the vehicle and thereby alters the vehicle's direction of flight. Although single, movable TVC nozzles provide adequate control over the vehicle's yaw and pitch, they do not provide any significant degree of roll control.
Accordingly, some vehicles are equipped with external aerodynamic fins for providing roll control. Such aerodynamic fins are rotatable about an axis perpendicular to the central longitudinal axis. These aerodynamic fins operate by transferring lateral aerodynamic drag forces acting on the fins to the vehicle. Because such forces are only present at sufficiently high velocities, aerodynamic fins are ineffective at low vehicle velocities and are totally ineffective in space. An additional disadvantage of such aerodynamic fins is that they are also ineffective at high angles of attack (i.e., angles of attack greater than about 30 degrees). Because many vehicles, particularly tactical missiles, are required to execute high-angle-of-attack maneuvers at low velocities, aerodynamic fins do not generally provide satisfactory roll control during such maneuvers.
Other conventional guidance mechanisms attempt to provide yaw, pitch, and roll control by placing movable blades within the flow of combustion products exiting the vehicle. One such mechanism includes three blades mounted within the vehicle. The blades include two smaller blades and one larger blade, with one of the smaller blades mounted on each side of the larger blade. The larger blade is partially rotatable about a first axis, and the two smaller blades are partially rotatable about a second axis perpendicular to the first axis. Each blade may be positioned independently of the other two blades. Thus, rotating the two smaller blades in the same direction alters the vehicle's pitch, while rotating the larger blade alters the vehicle's yaw. Tilting the two smaller blades in opposite directions alters the vehicle's roll.
However, in order to provide satisfactory yaw and pitch control, the blades in such a guidance mechanism must be relatively large. Large blades are undesirable because increasing the size of the blades in the exit path of the combustion products increases specific impulse losses, thereby decreasing the thrust generated by the rocket motor.
Thus, it would be an advancement in the art to provide a system for yaw, pitch, and roll control which provides satisfactory roll control at low vehicle velocities and during high-angle-of-attack maneuvers.
It would be a further advancement to provide such a system which does not decrease thrust by placing excessively large blades within the combustion product flow stream for yaw and pitch control.
Such a guidance system for yaw, pitch, and roll control is disclosed and claimed herein.